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Title: PERSISTENCE OF IMMUNITY TO TOXOPLASMOSIS IN PIGS VACCINATED WITH A NON- PERSISTENT STRAIN OF TOXOPLASMA GONDII

Author
item DUBEY JITENDER P - 1265-55-00
item BAKER D G - 1265-55-00
item DAVIS S W - 1265-55-00
item URBAN JOSEPH F - 1265-20-00
item SHEN SAMUEL K - 1265-55-00

Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: Infection by the protozoan parasite, Toxoplasma gondii, is widely prevalent in man and animals. Ingestion of tissue cysts in infected meat or ingestion of oocysts in food and water contaminated with infected cat feces are the 2 major means of transmission of T. gondii. Approximately 40% of adult human population in the U.S. has been exposed to T. gondii. There is no vaccine to control toxoplasmosis in animals or humans in the U.S. Scientists at the Beltsville Agricultural Research Center have found that a vaccine strain (RH) of T. gondii will infect pigs but will not persist in porcine tissues after 14 days. Immunity induced by the vaccine strain persists in pigs for at least 7 months. Results offer a hope of developing a vaccine to reduce the number of tissue cysts in tissues of pigs.

Technical Abstract: Persistence of the vaccine RH strain of Toxoplasma gondii was studied by bioassay and histologically in 14 pigs. Pigs were euthanatized between 2 and 76 days after IM inoculation with 100,000 T. gondii tachyzoites. Viable T. gondii derived from the RH strain was isolated by bioassay in mice inoculated with tissues of pigs euthanatized up to 14 days after vaccination. Except for fever, pigs vaccinated IM with the RH strain remained clinically normal. Two other pigs inoculated IV with 100,000 T. gondii tachyzoites of the RH strain became ill and 1 pig was comatose by 4 days after inoculation. These findings indicate that the route of vaccination may influence the response of pigs to toxoplasmosis. To evaluate protective immunity in pigs vaccinated with the RH strain, 16 age-matched pigs were divided into 2 groups of 8 pigs each. Eight pigs (group A) were vaccinated IM with 100,000 RH strain tachyzoites and 8 pigs (group B) were unvaccinated controls. Toxoplasma gondii was not isolated by bioassays from tissues of 5 of 8 vaccinated and challenge-inoculated pigs, but was recovered from all unvaccinated-challenged inoculated pigs. Results indicate that protective immunity persisted in pigs for at least 7 months after vaccination with the nonpersistent RH strain of T. gondii.